Lipid emulsions as a potential delivery system for ocular use of azithromycin

Objective: To obtain stable positively charged Azithromycin (AZI) emulsions with a mean droplet size of 120 nm for the treatment of eye diseases. Methods: The emulsions were obtained by using a suitable homogenization process. The physical stability was monitored by measuring the particle size, zeta potential, and visible appearance. The drug entrapment efficiency was measured by both ultracentrifugation and ultrafiltration methods. Compared with a phosphate solution of AZI, the stability profiles of AZI in lipid emulsions at various pH values were monitored by high-performance liquid chromatography. A pharmacokinetic study was performed to determine the drug levels in rabbit tear fluid using Ultra-performance liquid Chromatography–mass spectrometry. Results: Almost all the AZI in the lipid emulsion was distributed in the oil phase and small unilamellar liposomes without contact with water, thereby avoiding hydrolysis. The elimination of the AZI lipid emulsions in tear fluid was consistent with the basic linear pharmacokinetic characteristics. The AUC_0-t of the AZI lipid emulsion (1%, w/v) and aqueous solution drops (1%, w/v) was 1873.58 ± 156.87 and 1082.46 ± 179.06 μgh/ml respectively. Conclusions: This study clearly describes a new formulation of AZI lipid emulsion for ocular administration, and lipid emulsions are promising vehicles for ophthalmic drug delivery.